The New Sudoku Players' Forum

[tarek]

not with hard or very hard or very, very hard or extremely taxing puzzles for the experienced solvers amongst us.

Hi Luna,

So what defines these categories to you, where does the puzzle I posted fall into these categories.

Should I - Carcul suggested- ncrease the difficulty, or would the current setting be enough ?

[CathyW]

17 minutes is good then? I reduced it to 14 without the colouring but still using Simple Sudoku, though the fact I'd already done it may also have been a factor in that. It's towards the top end of times taken when using computer but I usually prefer to use pencil and paper and add candidates as required rather than eliminate them - though I'm becoming more comfortable with the latter!

I've only recently started using colouring and then only when using SS or Sadman. It's certainly not an easy technique for pencil and paper solvers.

Sequence of techniques - on computer with all candidates given I would check for singles, pairs, triplets and locked candidates initially, which is very easy when you can highlight the numbers. Then, probably, x-wings and simple colouring for further eliminations. Check again for singles, pairs, triplets and locked candidates. If simple colouring yields no further eliminations, sometimes it's at that point that I would see if multi-colouring would help. If it does, great - if not look for xy-wings or swordfish. I get stuck if puzzles require forcing chains.

On paper, it's slightly different - I don't think I've ever done a paper puzzle that required anything more difficult than x-wing, including the Sunday Times Superiors, though sometimes I've felt the need to dub a puzzle into a computer program to solve it.

For Times Fiendish or similar difficulty level the sequence is usually: check for singles that can be immediately placed - always at least one of these; enter paired candidates in boxes, rows and columns - depending on the puzzle this will often yield pairs and permit placement of other singles; enter other candidates as required until solution is found. I can usually manage the 'Difficult' level (as per the Times i.e. Pappocom Medium) without pencil marks. I let my daughter do the easy ones!

I won't be going to Lucca - family and work commitments would prevent that but I might be tempted by another Times competition if they do another one

Cathy

[CathyW]

Hummph To add to the above, I tried doing Tarek's puzzle on paper having dubbed into SS and removed all the candidates before printing it out. Hopelessly stuck even after nearly an hour - only 3 entries made, though I have got two independent swordfishes (4s). Currently at this position:

Code: Select all

 
  *-----------*
 |659|.31|.82|
 |...|...|9..|
 |4..|.9.|.5.|
 |---+---+---|
 |...|3..|.4.|
 |1..|...|...|
 |.6.|..8|..3|
 |---+---+---|
 |.1.|.7.|..5|
 |..5|1..|...|
 |28.|945|.71|
 *-----------*


{6}      {5}      {9}      {47}     {3}      {1}      {47}     {8}      {2}     
{378}    {237}    {12378}  {25678}  {2568}   {2467}   {9}      {13}     {467}   
{4}      {237}    {12378}  {2678}   {9}      {267}    {13}     {5}      {67}     
{5789}   {279}    {278}    {3}      {1256}   {2679}   {125678} {4}      {6789}   
{1}      {23479}  {2378}   {2567}   {256}    {24679}  {25678}  {269}    {6789}   
{579}    {6}      {247}    {2457}   {125}    {8}      {1257}   {129}    {3}     
{39}     {1}      {346}    {268}    {7}      {236}    {23468}  {2369}   {5}     
{379}    {3479}   {5}      {1}      {268}    {236}    {2368}   {2369}   {4689}   
{2}      {8}      {36}     {9}      {4}      {5}      {36}     {7}      {1}     
     


I know there's plenty of eliminations to be done - because I did it yesterday - but I can't see them on paper

Editing after viewing this post - just spotted the locked 6s in box 3!

[tarek]

You've reached the point where all the fun is, 2 swordfishes, 2 x-wings & a quad (depending on the techniques used).

The generator assumes that the solver will pick the simplest technique next (rather than a BEST MOVE or the Pathway of techniques the human solver would normally use).

That is why (at the moment), there is hardly any example of a quintuple or a jellyfish in my generated collection.

[CathyW]

Hmm - still can't see the x-wing or the quad on paper - being able to highlight particular numbers on the computer makes things so much easier!

However, I wanted to analyse a bit further how I'd done this puzzle the first time in what would seem to be a good time using SS. I didn't previously keep a log but the key thing would seem to be what I call bivalue cell eliminations - I haven't figured out WHY it works, maybe related to xy-wings, but hopefully someone will be able to explain. I should add that the first time I did the puzzle I hadn't spotted the swordfishes of 4s and used colouring for some eliminations.

From the position above:
There are two bivalue cells in box 7, both of which contain 3. You can eliminate the rest of the 3s in box 7. Now previously I would have thought that r7c1 could be 9 and r9c3 could be 6 so the 3s could be anywhere else in the unfilled cells of box 7.

Having done that, the candidate grid is:

Code: Select all

{6}      {5}      {9}      {47}     {3}      {1}      {47}     {8}      {2}     
{378}    {237}    {12378}  {25678}  {2568}   {2467}   {9}      {13}     {467}   
{4}      {237}    {12378}  {2678}   {9}      {267}    {13}     {5}      {67}     
{5789}   {279}    {278}    {3}      {1256}   {2679}   {125678} {4}      {6789}   
{1}      {23479}  {2378}   {2567}   {256}    {24679}  {25678}  {269}    {6789}   
{579}    {6}      {247}    {2457}   {125}    {8}      {1257}   {129}    {3}     
{39}     {1}      {46}     {268}    {7}      {236}    {23468}  {2369}   {5}     
{79}     {479}    {5}      {1}      {268}    {236}    {2368}   {2369}   {4689}   
{2}      {8}      {36}     {9}      {4}      {5}      {36}     {7}      {1}     


Next, using the bivalue cells r7c3 and r1c7, we can eliminate 4 in r7c7. Because the swordfishes of 4s had been spotted earlier, this is a key move and enables the rest of the puzzle to be solved with singles and pairs very quickly

Think I need a different puzzle now - maybe the Shogun in the Times supplement today?

[lunababy_moonchild]

not with hard or very hard or very, very hard or extremely taxing puzzles for the experienced solvers amongst us.

Hi Luna,

So what defines these categories to you, where does the puzzle I posted fall into these categories.

Should I - Carcul suggested- ncrease the difficulty, or would the current setting be enough ?

Hi Tarek

I don't know! I just know that there are very few books available - Carol Vorderman has just released one and Nikoli also have one through Hamlyn - on anything harder than the Pappocom Fiendish puzzles available, which is a constant annoyance to accomplished solvers like Tso, for example.

I'm still in the realms of Nikoli easy at the moment, so have it all to do as of yet.

Tell you what, if you can generate a puzzle that gives Tso a run for his money, you've got a hold of something special. How you would do that, I don't know

Not much help there then !

Luna

[tarek]

Well Cathy there went through it like a hot knife through butter. If solvers use ultralcolouring or techniques above xy wing then it would definitely cut times shorter.

The puzzle I posted does not require those techniques, so for a person who does not know simple colouring, ultra colouring nor forcing chains......... he could still solve it.

This difficulty level was chosen for that specific person as he would use all his resources to solve it .

The next level of difficulty probably would be techniques above xy wing & below forcing chains (xyz, colouring, ultra colouring,.....), & then different levels of forcing chains.

That makes it 3 books. Books in my opinion that would not sell unless easier puzzles for the rest of the public were incorporated.

[9X9]

I don't normally look at the forums these days, I have too much else to do, but stocku has mentioned the comments on the book to me so thanks for the candid thoughts, even if some of them are less than fair on the author in my opinion.

To be honest, having bought it, scanned it quickly, thought it looked promising and then filed it in our bookcase for future reference, I haven't been near it since. In the interim, we've moved house and still haven't unpacked all the boxes, and now have a three week-old baby together with our one year-old, both of whose staple diet is time!!

Hopefully, I'll get to it in due course and do what I intended at the start, which is to try the "hardest" first although, judging from your views, it may not occupy me over-long. Still, it's the only book I've so far personally seen which deals with chains in any way and in understandable language for the lay solver into the bargain, and if they are not quite the soi-disant "nice" loops which pre-occupy Carcul in these forums, then so much the better for me, since these seem so far removed from the Su Doku as "a thing of beauty" which Wayne describes in his own book, "Ultimate Su Doku", as to render them a virtual anathema. Also, the "Sudoku Genius" title spine looks seriously impressive, perched between my copies of "What They Really Teach You At The Harvard Business School" and "Taking Chances" - "winning with probability"!!

My best wishes to you all.

[Pat]

this book only confirms that hard puzzles cannot be found in published books.
Regarding the last and (theoretically) toughest puzzle of this book, it's one of the most simple that I have solved.

Carcul, you are an expert solver - what you consider a simple puzzle may not be so simple to me!

perhaps someone would post just one sample puzzle from this book?

~ Pat

[CathyW]

From the position above:
There are two bivalue cells in box 7, both of which contain 3. You can eliminate the rest of the 3s in box 7.

It would appear from discussion of xy-chains in another thread in the Advanced Solving Techniques forum that this was a happy coincidence! But I'm sure there must be a reason somewhere that permits the eliminations - Simple Sudoku allowed them! (If something is not OK, I have the option checked for invalid moves to be made known.) I concede that simply having two bivalue cells, both containing 3, in the same unit, isn't sufficient though I think they must be part of the equation. It definitely isn't an xy-chain - there aren't enough bivalue cells at that point in the puzzle, but perhaps there is a forcing chain involving them.

Anyone?

[tarek]

From the position above:
There are two bivalue cells in box 7, both of which contain 3. You can eliminate the rest of the 3s in box 7.

why not go for the box 3 column 9 elimination, then you will see the x-wing then the 2 swordfishes

To me the 3s elimination at box 7 will come eventually at the end using simpler techniques.

[Carcul]

Hi Pat.

Here are some samples from the book (the book is divided in nine levels, with level 9 the hardest). This is from level 1:

Code: Select all

 . . 8 | 5 . . | 6 . .
 2 3 . | . . 8 | . 4 .
 . . 6 | . 7 . | . . .   
-------+-------+------
 . 1 7 | . . . | . . .
 5 2 . | . . . | . 6 8
 . . . | . . . | 2 3 .
-------+-------+------
 . . . | . 3 . | 1 . .
 . 7 . | 6 . . | . 5 9
 . . 4 | . . 1 | 8 . .


Level 3:

Code: Select all

 2 . 7 | . . 3 | . 8 .
 . 5 . | . 9 . | . . 6
 . . . | . . . | . . 9   
-------+-------+------
 . 4 . | 2 . . | . . .
 . . 8 | 5 . 1 | 6 . .
 . . . | . . 4 | . 3 .
-------+-------+------
 4 . . | . . . | . . .
 5 . . | . 7 . | . 2 .
 . 3 . | 9 . . | 4 . 5


Level 7:

Code: Select all

 4 1 . | 6 . . | . 5 8
 9 . . | 5 . . | . . .
 . . . | 4 . . | . 2 6   
-------+-------+------
 . 5 . | . . . | . . .
 . . 9 | 3 . 2 | 5 . .
 . . . | . . . | . 7 .
-------+-------+------
 8 4 . | . . 3 | . . .
 . . . | . . 4 | . . 7
 5 7 . | . . 1 | . 3 4


Level 8:

Code: Select all

 3 . . | 5 . 1 | . . 9
 . . . | . . . | . 2 .
 6 . . | 8 . 2 | . . 7   
-------+-------+------
 . 4 . | . . . | . . 1
 . 6 9 | . . . | 3 7 .
 2 . . | . . . | . 5 .
-------+-------+------
 1 . . | 2 . 3 | . . 6
 . 7 . | . . . | . . .
 8 . . | 6 . 4 | . . 5


And this is the one that makes level 9:

Code: Select all

 . . . | . . . | 5 4 .
 . . 6 | . . . | . . 8
 4 2 . | 7 . . | . . .   
-------+-------+------
 . . 3 | 6 7 . | . . 2
 . . . | 1 . 8 | . . .
 9 . . | . 4 2 | 1 . .
-------+-------+------
 . . . | . . 3 | . 6 7
 5 . . | . . . | 9 . .
 . 9 2 | . . . | . . .


Have fun.

Regards, Carcul

[Heuresement]

If I may jump in here, I just happened to be looking for a more fiendish puzzle to do today (generally on Mondays and Tuesdays, when The Times doesn't do Fiendish), and so tried the Level 9 sample on paper, and I would like to thank you for the opportunity.

As far as I remember, I found one triple / hidden double, and most of the rest were doubles. I would rate it almost on par with a Pappacom v.hard.

btw I have been practising doing all puzzles (except for the Times Superior - Pappacom v.hard) without using pencilmarks (ever since somebody once accused me of using the Voorderman technique), and I was able to complete this one with pencilmarks, which was why I rated this one slightly easier than a Sunday Times Superior ( Pappacom v.hard).

Once I have completed all the fiendish/superior puzzles in the Ultimate Su Doku book (which is the best book ever especially in waiting rooms and such like), this "Sudoku Genius" book does look a good one to try.

[tarek]

Once I have completed all the fiendish/superior puzzles in the Ultimate Su Doku book (which is the best book ever especially in waiting rooms and such like), this "Sudoku Genius" book does look a good one to try.

Hi Heuresement,

have you tried the puzzle I posted in this thread?
The reason was to see if there was demand for a more difficult puzzle?

Is my puzzle your cup of tea ????

[Heuresement]

Hi Tarek!

I am afraid that I became stuck quite quickly, and so had to resort to marking candidates using a pencil. I saw the swordfish, but failed to remove all the candidate 4s, and was then fully stuck. I started again, and this time, used the swordfish correctly, but couldn't spot where to go next, so I ended up having to cheat by reading the earlier posts. I didn't spot the quad until I loaded it into SS, and then it was all straightforward.

In order to be able to do puzzles of this difficulty with or without using pencil candidates, I clearly need more practice, so that I am able to spot the swordfishes/x-wings much quicker. I believe that I am generally proficient at spotting triples, naked or otherwise, but the naked quad was something else . The fact that all these techniques were combined in the one puzzle made it enjoyable. I suppose that the good thing is that once I had seen all the steps I realised that I could have found them myself without assistance.

Do you have another example like this? I will find the time to complete it fully on paper, if I am able